Processes and systems for refining fuel gas

ABSTRACT

Processes and systems are provided for refining fuel gas. The processes involve first and second water wash stages, before and after a caustic wash stage, in which fuel gas is contacted with water for removing amine and caustic compounds from the fuel gas. The systems for refining LPG comprise a first water wash vessel and a caustic wash vessel, followed by a second water wash vessel, wherein the water wash vessels are each adapted for contacting the LPG with water to remove amine and caustic compounds therefrom.

TECHNICAL FIELD

The technical field generally relates to processes and systems forrefining fuel gas, and more particularly relates to processes andsystems for the removal of sulfur compounds from fuel gas using an amineand a caustic to produce a refined fuel gas substantially free ofresidual amine and residual caustic.

BACKGROUND

Fuel gases are a category of hydrocarbon mixtures in which thehydrocarbons have from one to four carbons per molecule (i.e., C₁-C₄hydrocarbons). Fuel gases are gaseous under normal conditions and usefulas sources of energy and light when burned. In particular, natural gasis one type of fuel gas primarily comprised of methane (C₁hydrocarbons). Mixtures containing primarily C₃-C₄ hydrocarbons (i.e.,propane and butane) are also gaseous under normal conditions, but aresometimes converted to liquefied petroleum gas (LPG) by pressurizationto convert them to liquid form, which reduces volume and facilitatesstorage, delivery and use. LPGs are relatively clean burning fuelsuseful for heating, cooking, and an alternative vehicle fuel, as well asan aerosol propellant and a refrigerant.

Particularly when derived from petroleum, fuel gases often containundesirable components including sulfur compounds and carbon dioxide,among others, which adversely affect various refining steps and end useapplication. More particularly, for example, fuel gases are oftentreated with an amine compound to remove hydrogen sulfide (H₂S) andcarbon dioxide (CO₂), followed by removal of carbonyl sulfide (COS) andpossibly additional H₂ 5 by contact with caustic in a prewash unit.After removal of H₂S, CO₂, and COS, mercaptans (R-SH) are removed fromthe fuel gas, such as by extraction in the presence of caustic, followedby conversion of the extracted mercaptans to organic disulfides andregenerated caustic that can be recycled and reused.

Amine solubility in fuel gases, as well as amine entrainment in theprocess streams of fuel gas refinement processes, results in thepresence of amines in the effluent of the amine treatment stage as wellas in subsequent process stages, which is often referred to as aminecarryover. Amine carryover in fuel gas refining processes is one of themajor causes of amine losses and serious problems in stages downstreamof the amine treatment stage. For example, when amines are mixed withcaustic solutions in the presence of hydrocarbons, emulsions are formedthat adversely affect the composition of the final fuel gas product,cause higher caustic consumption and corrosion of carbon steel indownstream process units, and require operation at lower hydrocarbonflow rates that decreases production. Additionally, any amines remainingin the effluent of the caustic prewash stage, when fed to the mercaptanextraction stage, reduces the capability of the mercaptan extractionstage to produce refined fuel gas having the required low nitrogencontent. Amine carryover is often exacerbated when refining LPG derivedfrom fluid catalytic cracking processes or from the coker units ofatmospheric or vacuum distillation processes.

Following amine treatment for removal of H₂S and CO₂, but prior tocontact with caustic for removal of COS, fuel gas is sometimes subjectedto a water wash to remove soluble amines and reduce formation ofunwanted emulsions during the caustic prewash step. However, aminecarryover remains an issue even in processes that include a water washstage prior to caustic prewash, or knockout (KO) drums for removingentrained amines, or both, since such apparatus typically does notinclude internal features to enhance separation between amine and spentwater from the hydrocarbons.

Accordingly, it is desirable to develop processes for refining fuel gasthat provide improved removal of unwanted compounds. In addition, it isdesirable to provide processes for refining fuel gas whereinsubstantially all the amine is removed prior to subjecting the fuel gasto treatment for mercaptan removal. Furthermore, other desirablefeatures and characteristics of the present invention will becomeapparent from the subsequent detailed description of the invention andthe appended claims, taken in conjunction with the accompanying drawingsand this background of the invention.

BRIEF SUMMARY

Processes and systems are provided for refining fuel gas. An exemplaryembodiment of the process comprises: providing a fuel gas comprising anamine compound; contacting the fuel gas with water in a first water washstage to remove at least a portion of the amine compound therefrom andproduce a washed fuel gas; contacting the washed fuel gas with either acaustic to remove acid gas (H₂S, CO₂, or both) or a blend of a causticand an amine to remove both acid gas and carbonyl sulfide (COS) from thewashed fuel gas and produce a caustic treated fuel gas comprisingresidual amine and residual caustic. The process further comprisescontacting the caustic treated fuel gas with water in a second waterwash stage to remove residual amines and residual caustic therefrom andproduce a rewashed fuel gas substantially free of amines and caustic.

In another exemplary embodiment, a process for refining fuel gascomprising: contacting a fuel gas with an amine compound to removehydrogen sulfide (H₂S), carbon dioxide (CO₂), or both, therefrom andproduce an amine treated fuel gas comprising an amine compound; andcontacting the amine treated fuel gas with water to remove at least aportion of the amine compound therefrom and produce a washed fuel gas.The process further comprises, contacting the washed fuel gas witheither a caustic to remove acid gas or a blend of a caustic and an amineto remove both acid gas and carbonyl sulfide (COS) from the washed fuelgas and produce a caustic treated fuel gas comprising residual amine andresidual caustic; contacting the caustic treated fuel gas with water toremove residual amines and residual caustic therefrom and produce arewashed fuel gas substantially free of amines and caustic; and removingmercaptans from the rewashed fuel gas.

In still another embodiment, a system for refining LPG comprising: afirst water wash vessel capable of receiving and contacting LPG withwater to remove an amine compound from the LPG and produce a washed LPG;a vessel capable of receiving and contacting the washed LPG with eithera caustic to remove acid gas or a blend of a caustic and an amine toremove both acid gas and carbonyl sulfide (COS) from the washed fuel gasand produce a caustic treated LPG comprising residual amine; and asecond water wash vessel capable of receiving and contacting the caustictreated LPG with water to remove residual amine therefrom and produce arewashed LPG substantially free of amines.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and wherein:

FIG. 1 is a block diagram showing an exemplary embodiment of a refiningsystem including first and second water wash stages that are verticallyoriented; and

FIG. 2 is a block diagram showing another exemplary embodiment of arefining system including first and second water wash stages that arehorizontally oriented.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the processes and systems contemplated herein, orthe application and uses thereof. Furthermore, there is no intention tobe bound by any theory presented in the preceding background or thefollowing detailed description.

The processes and systems contemplated and described herein are directedto removal of unwanted compounds, including one or more of H₂S, CO₂,COS, and mercaptans, from fuel gas, as well as removing amine compoundsand caustic that are often used to remove the aforesaid unwantedcompounds but which interfere with other refining stages. The processesand systems contemplated and described herein are suitable for refiningany fuel gas, including natural gas (methane), ethane, mixtures ofmethane and ethane (i.e., mixtures of C₁-C₂ hydrocarbons), propane,butane, mixtures of propane and butane (i.e., mixtures of C₃-C₄hydrocarbons), and LPG (liquefied mixtures of C₃-C₄ hydrocarbons). Morespecifically, the processes and systems described hereinbelow aresuitable for refining liquid phase fuel gases such as LPG, as well asfuel gases that are in gaseous form such as the others types of fuelgases listed above. The fuel gas may be derived from any one or more ofvarious sources including, without limitation, fractionation processesand apparatus, straight run petroleum refining processes and apparatus,fluidized catalytic cracking processes and apparatus, and thermalcracking processes and apparatus (e.g. coker units).

Additionally, the refining of fuel gas generally involves varioustreatments, operations, stages, techniques and methods for achievingvarious goals, all of which are ultimately aimed at producing purehydrocarbon products having desired characteristics for particular enduses. Accordingly, it should be understood that the processes andsystems contemplated and described herein may exist, and be performed oroperated, within the context of larger refining processes and systems,or more complex refining processes and systems, or both.

In an exemplary embodiment, the process for refining fuel gascontemplated and described herein comprises providing a fuel gascomprising an amine compound, and contacting that fuel gas with water ina first water wash stage to remove at least a portion of the aminecompound therefrom and produce a washed fuel gas. In the first waterwash stage, after contacting the fuel gas and water, the amine compoundmigrates from the fuel gas (organic phase) and is dissolved into thewater (aqueous phase) and aqueous and organic phases are separated, suchas by gravity separation where both phases are liquid (as when refiningLPG), or liquid-gas phase separation where the aqueous phase is liquidand the organic phase is gaseous (as when refining a gaseous fuel gas).The resulting organic phase is the washed fuel gas that is subjected tofurther processing, and the resulting aqueous phase can be processed orrecycled, or both, as desired.

The washed fuel gas from the first water wash stage is then contacted,in a caustic wash stage, with either a caustic to remove acid gas (i.e.,H₂S, CO₂, or both) or a blend of a caustic and an amine to remove bothacid gas and carbonyl sulfide (COS) from the washed fuel gas and producea caustic-treated fuel gas. In either case, suitable caustic includessodium hydroxide (NaOH) and potassium hydroxide (KOH), with NaOH beingthe more common choice. Where a blend of caustic and amine is used, theamine is comprised of primary amines, secondary amines, or mixturesthereof. Since undesirable emulsions are formed when amines are mixedwith caustic solutions in the presence of hydrocarbons, removal ofresidual amine compounds in the fuel gas before contacting the fuel gaswith caustic to remove COS improves the effectiveness and efficiency ofthe COS removal during the caustic wash stage. However, the first waterwash stage removes a majority of the amine compound which improvesperformance of the caustic wash stage, but the caustic treated fuel gasstill contains residual amine compound, as well as residual caustic fromthe caustic wash stage. Furthermore, additional amine compound may beadded during the caustic wash stage to assist in removal of unwantedcompounds, such as H₂S, in the washed fuel gas, which consequentlyincreases the total amine compound content of the caustic treated fuelgas. Any additional amine compound used in the caustic wash stage may bethe same or different from the amine compound present in the fuel gasprior to the first water wash stage.

Removal of substantially all residual amine compounds is important fortoday's refining processes to produce hydrocarbon streams having therequired low levels of unwanted compounds to avoid downstreamoperational and product quality issues where the fuel gas will undergofurther refinement stages. Consequently, the caustic treated fuel gascontaining residual amine compound is contacted with water in a secondwater wash stage to remove residual amine therefrom and produce arewashed fuel gas substantially free of amine compounds. The secondwater wash phase operates substantially the same as the first water washstage, except that in the second water wash stage, the caustic alsomigrates from the fuel gas (organic phase) to the water (aqueous phase)so that when the aqueous and organic phases are formed and separated,the aqueous phase contains amine compound and caustic.

“Substantially free of amine compounds,” means that any amines presentin the rewashed fuel gas are below the amount that causes downstreamoperational and product quality issues. For example, “substantially freeof amine compounds” as used herein, means that the rewashed fuel gascomprises no more than about 60 parts per million by weight (ppm) totalamine compound. For example, without limitation, the rewashed fuel gasmay comprise no more than about 50 ppm total amine compound, or no morethan about 30 ppm total amine compound, or even no more than about 10ppm total amine compound.

Similarly, “substantially free of caustic compounds,” means that anycaustic present in the rewashed fuel gas are below the amount that causedownstream operational and product quality issues. More particularly,and independently of the amine content, “substantially free of causticcompounds” as used herein, means that the rewashed fuel gas comprises nomore than about 60 ppm total caustic compound. For example, withoutlimitation, the rewashed fuel gas may comprise no more than about 50 ppmtotal caustic compound, or no more than about 30 ppm total causticcompound, or even no more than about 10 ppm total caustic compound.

In some embodiments, such as when the fuel gas being refined is LPG,during either the first water wash stage or the second water wash stage,or both, the fuel gas (or caustic treated fuel gas, as applicable) andwater are also contacted with coalescing material to enhanceaqueous-organic phase separation and removal of the amine compound fromthe fuel gas. More particularly, the coalescing material may be anymaterial known now or in the future to be hydrophilic and facilitateaqueous-organic phase separation. For example, without limitation, thecoalescing material may be mesh made of metal such as stainless steel,and may further be coated with a hydrophilic material such as a polymer.The coalescing material may be present in a layer that is from about15.24 centimeters (cm) (6 inches) to about 60.96 cm (24 inches) thick.Additionally, the coalescing material used in each of the first andsecond water wash stages may be the same or different from one another,in composition as well as physical form and size.

When the fuel gas being refined is a gaseous fuel gas such as includingnatural gas (methane), ethane, propane, butane, or mixtures of two ormore of these hydrocarbons, the fuel gas (or caustic treated fuel gas,as applicable) and water forms a liquid-gas system for which coalescingmaterial is less advantageous. Accordingly, in embodiments where thefuel gas is a gaseous type of fuel gas, the fuel gas (or the caustictreated fuel gas, if applicable) and water may also be contacted with aninternal device positioned within one or both of the first and secondwater wash stages, for enhancing aqueous-organic phase separation andremoval of the amine compound from the gaseous organic phase fuel gas.The internal device is not particularly limited and may be any internaldevice known now or in the future that facilitates phase separation inliquid-gas systems. Suitable internal devices include, for example, oneor more bubble trays, sieve trays, packed beds and other contactingdevices.

Furthermore, it is noted that when the fuel gas is a gaseous type offuel gas that is being refined, contacting the fuel gas with water inthe first water wash stage, contacting the resulting washed fuel gaswith caustic in a caustic wash stage, then contacting the resultingcaustic treated fuel gas with water in the second water wash stage mayall be performed in the same vessel, such as a single vertical column Asuitable single vessel would, of course, be capable of allowing thegaseous fuel gas to flow from one end to an opposite end of the vessel,while also allowing the fuel gas to sequentially contact the water,caustic and then water again to produce a rewashed fuel gas suitable forfurther refinement. In some embodiments, the vessel is capable of alsocontacting the liquid-gas mixture comprising gaseous fuel gas and waterwith internal devices positioned within the vessel to enhance phaseseparation during the first water wash stage, caustic wash stage, andsecond water wash stage occurring therein.

In another exemplary embodiment, regardless of whether the fuel gas isgaseous or LPG, providing a fuel gas comprising an amine compoundincludes first providing a fuel gas comprising unwanted compoundsincluding hydrogen sulfide (H₂S), carbon dioxide (CO₂), and carbonylsulfide (COS) and contacting that fuel gas with an amine compound toremove hydrogen sulfide (H₂S), carbon dioxide (CO₂), or both, therefrom.Contacting the fuel gas with an amine compound produces an amine treatedfuel gas comprising an amine compound. Contacting the fuel gas with anamine compound may, for example, be performed by absorption with anaqueous solution comprising the amine compound. Where the fuel gas isLPG, the absorption will occur as a liquid-liquid absorption process. Insuch embodiments where fuel gas containing unwanted compounds iscontacted with an amine compound, the resulting amine treated fuel gas,which consequently comprises an amine compound, is contacted with waterin the first water wash stage. The amine compound may be any aminecompound known now or in the future to be a good solvent for H₂S and CO₂and at least partially soluble in aqueous solution. Suitable aminecompounds include one or more compounds chosen from, for example withoutlimitation, monoethanolamine (MEA), diethanolamine (DEA), diglycolamine(DGA), methyl diethanolamine (MDEA), MDEA-based solvents, anddiisopropylamine (DIPA), among others.

In still another exemplary embodiment, the process further comprisesremoving mercaptans from the rewashed fuel gas. Removal of mercaptansmay be accomplished by any technique known now or in the future. Forexample, mercaptans (RSH) may be removed from the rewashed fuel gas by atwo stage process in which the first stage involves contacting therewashed fuel gas with caustic (MOH, where M is sodium, Na, orpotassium, K) in the presence of a catalyst capable of catalyzing theconversion and extraction of the mercaptan in metal salt form (M-SR)into an aqueous caustic solution. Suitable catalysts are commerciallyavailable, for example, from UOP LLC of Des Plaines, Ill., USA. Inaddition to the aqueous caustic solution containing the mercaptanderivatives (M-SR), the first stage also produces a refined fuel gasproduct. In the second stage, generally referred to as regeneration, theaqueous caustic solution containing the mercaptan derivatives (M-SR) isheated and oxidized to form insoluble disulfides (RSSR) and regeneratedcaustic (MOH). Moreover, in some embodiments such as where the fuel gasis a gaseous phase material, the above-described three contacting steps(first water wash, caustic wash, and second water wash), as well asremoving mercaptans from the rewashed fuel gas, may all be performed inthe same vessel as described earlier hereinabove.

Amines entering the mercaptan removal phase of the refining process aregenerally not removed or otherwise altered and, therefore, often causefuel gas products having unacceptably high nitrogen content, as well aspotential process upsets in stages downstream of the mercaptan removalphase. Thus, employing the second water wash stage to remove additionalresidual amine compounds prior to subjecting the caustic treated andrewashed fuel gas to mercaptan removal processes improves theeffectiveness and efficiency of the mercaptan removal process as well asdownstream refining stages.

A system for refining LPG will now be described in detail with referenceto FIGS. 1 and 2 which provide schematic diagrams of such systems. In anexemplary embodiment, the system 10, 110 for refining LPG comprises afirst water wash vessel 12, 112, a caustic wash vessel 14, 114 and asecond water wash vessel 16, 116. More particularly, the first waterwash vessel 12, 112 is capable of receiving and contacting LPG 18, 118with water (provided via lines 46, 48, 146, 148, respectively) to removean amine compound from the LPG 18, 118 and produce a washed LPG 20, 120.

The caustic wash vessel 14, 114 is in fluid communication with, andlocated downstream of, the first water wash vessel 12, 112. The causticwash vessel 14, 114 is capable of receiving and contacting the washedLPG 20, 120 with a caustic to remove acid gas, or a blend of caustic andamine (provided via line 15, 115, respectively) to remove both acid gasand carbonyl sulfide (COS) from the washed LPG and produce a caustictreated LPG 22, 122 comprising residual amine. In either case, thecaustic is a strong base selected from sodium hydroxide (NaOH) andpotassium hydroxide (KOH). Where a blend of caustic and amine is used,the amine is comprised of primary amines, secondary amines, or mixturesthereof. The second water wash vessel 16, 116 in fluid communicationwith, and located downstream of, the caustic wash vessel 14, 114. Thesecond water wash vessel 16, 116 is capable of receiving and contactingthe caustic treated LPG 22, 122 with water (not shown) to removeresidual amine and residual caustic therefrom and produce a rewashed LPG24, 124 substantially free of amine and caustic compounds. The firstwater wash vessel 12 and second water wash vessel 16 may each beoriented vertically as shown in FIG. 1, or they 112, 116 may be orientedhorizontally as shown in FIG. 2. “Substantially free of amine compounds”has the same meaning as stated hereinabove.

As mentioned above in connection with the first and second water washstages, coalescing material may also be contacted with the LPG and waterto facilitate aqueous-organic phase separation. Accordingly, as shown ineach of FIGS. 1 and 2, either or both of the first and second water washvessels 12, 112, 16, 116 may include coalescing material 26, 126, 28,128 in the interiors thereof, respectively. Suitable coalescingmaterials are as described above. The coalescing material 26, 126 in theinterior of the first water wash vessel 12, 112 may be the same ordifferent, in composition as well as physical form and size, from thecoalescing material 28, 128 in the interior of the second water washvessel 16, 116. As shown in FIG. 1, when the first and second water washvessels 12, 16, are oriented vertically, the coalescing material 26, 28is oriented horizontally. When the first and second water wash vessels112, 116 are oriented horizontally, as shown in FIG. 2, the coalescingmaterial 126, 128 is oriented vertically.

Regardless of whether they are oriented vertically or horizontally, orwhether the include coalescing material, each of the first and secondwater wash vessels 12, 112, 16, 116 produces spent wash water 42, 142,44, 144, respectively. The spent wash water 42, 142, 44, 144 may be sentfor further processing, or recycled to one or both of the first andsecond water wash vessels 12, 112, 16, 116, as shown in FIGS. 1 and 2.Furthermore, fresh water may be provided to one or both of the first andsecond water wash vessels 12, 112, 16, 116 via fresh water inlets 46,146, 48, 148, respectively, which are in direct or indirect fluidcommunication with the first and second water wash vessels 12, 112, 16,116, respectively.

In some embodiments, as shown in FIGS. 1 and 2, the system 10, 110 alsocomprises an absorber 30, 130 capable of receiving and contacting LPG32, 132 with an amine compound (not shown) to remove H₂S, CO₂, or both,from the LPG 32, 132 and produce an amine treated LPG 34, 134 comprisingresidual amine compounds. In such embodiments, the first water washvessel 12, 112 is in fluid communication with the absorber 30, 130 forreceiving and contacting the amine treated LPG 34, 134 with water (notshown). Suitable amine compounds are as described above. In suchembodiments, i.e., systems that include an absorber upstream of thefirst water wash stage, the amine treated LPG 34, 134 serves as the LPG18, 118 that is provided to the first water wash stage for contactingwith water.

In still other embodiments, the system 10, 110 for refining LPG furthercomprises apparatus capable of removing mercaptans from the rewashed LPG24, 124. For example, as shown in FIGS. 1 and 2, such apparatus maycomprise an extractor 36, 136 capable of receiving and contacting therewashed LPG 24, 124 with caustic (MOH, where M is sodium, Na, orpotassium, K). The extractor 36, 136 generally comprises a catalyst (notshown per se) capable of catalyzing the conversion and extraction of themercaptans, as described above. The extractor 36, 136 produces an LPGproduct 38, 138 and an aqueous caustic solution 40, 140 comprising themercaptan in metal salt form, as also previously described above. Thesystem 10, 110 may further comprise a regeneration vessel (not shown)capable of receiving the aqueous caustic solution 40, 140 from theextractor 36, 136 and heating and oxidizing the aqueous caustic solution40, 140 to form insoluble disulfides and regenerated caustic (notshown).

Although not shown in the figures, it should be appreciated that thesystem 10, 110 shown in FIGS. 1 and 2 may be modified for refining fuelgas in gaseous form, such as natural gas (methane), ethane, mixtures ofmethane and ethane (i.e., mixtures of C₁-C₂ hydrocarbons), propane,butane, mixtures of propane and butane (i.e., mixtures of C₃-C₄hydrocarbons), and mixtures of C₁-C₄ hydrocarbons. Such modifications tothe system 10 shown in FIG. 1 will now be discussed in further detail.More particularly, in an exemplary embodiment of a modified system (notshown per se) for refining fuel gas, the first water wash vessel 12, thecaustic wash vessel 14, and the second water wash vessel 16 are insteadreplaced by a vessel, such as a multi-stage column, capable of receivingfuel gas in a bottom portion thereof and allowing the fuel gas to flowupward through the column Furthermore, the multi-stage column comprisesa first water wash zone located proximate the bottom portion of thecolumn, a caustic (or caustic-amine blend) wash zone located in a middleportion of the column, and a second water wash zone located an upperportion of the column Instead of coalescing material (see 26, 126, 28,128 in FIG. 1), the first and second water wash zones of the multi-stagecolumn may each include internal devices such as bubble trays (not shownper se) to facilitate contact between the gaseous fuel gas and water ineach water wash stage and, thereby enhance phase separation.Additionally, a system (not shown) for refining gaseous fuel gas mayinclude an absorber adapted for receiving and contacting gaseous fuelgas with a liquid aqueous solution containing an amine compound. Forexample, such an absorber may comprise a plurality of trays to increasegas-liquid phase contact between the gaseous fuel gas and the aqueousamine solution.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention. It being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims.

What is claimed is:
 1. A process for refining fuel gas comprising:providing a fuel gas comprising an amine compound; contacting the fuelgas with water in a first water wash stage to remove at least a portionof the amine compound therefrom and produce a washed fuel gas;contacting the washed fuel gas with either a caustic to remove acid gasor a blend of a caustic and an amine to remove both acid gas andcarbonyl sulfide (COS) from the washed fuel gas and produce a caustictreated fuel gas comprising residual amine and residual caustic; andcontacting the caustic treated fuel gas with water in a second waterwash stage to remove residual amines and residual caustic therefrom andproduce a rewashed fuel gas substantially free of amine and caustic. 2.The process of claim 1, wherein contacting the fuel gas with water in afirst water wash stage further comprises using a coalescing material. 3.The process of claim 1, wherein contacting the caustic treated fuel gaswith water in a second water wash stage further comprises using acoalescing material, which may be the same or different from thecoalescing material used in the first water wash stage.
 4. The processof claim 1, wherein providing the fuel gas comprises contacting a fuelgas with an amine compound to remove hydrogen sulfide (H₂S), carbondioxide (CO₂), or both, therefrom and produce an amine treated fuel gascomprising an amine compound, and wherein the amine treated fuel gas isthen contacted with water.
 5. The process of claim 4, wherein contactingthe fuel gas with an amine compound is performed by absorption with anaqueous solution comprising the amine compound.
 6. The process of claim4, wherein providing the fuel gas comprises providing liquefiedpetroleum gas (LPG).
 7. The process of claim 1, wherein contacting thewashed fuel gas with caustic is performed using a strong base selectedfrom sodium hydroxide and potassium hydroxide as the caustic.
 8. Theprocess of claim 1, wherein a single vessel is used for contacting thefuel gas with water to produce the washed fuel gas, and for contactingthe washed fuel gas with a caustic to produce the caustic treated fuelgas comprising residual amine and residual caustic, and for contactingthe caustic treated fuel gas with water in a second water wash stage tothe rewashed fuel gas substantially free of amine and caustic.
 9. Theprocess of claim 8, wherein the fuel gas is chosen from: methane,ethane, propane, isobutene and mixtures thereof.
 10. The process ofclaim 1, further comprising removing mercaptans from the rewashed fuelgas.
 11. The process of claim 10, wherein removing mercaptans from therewashed fuel gas comprises contacting the rewashed fuel gas with anaqueous caustic solution in the presence of a catalyst to produce arefined fuel gas product and an aqueous solution comprising mercaptanderivatives; and heating and oxidizing the aqueous solution comprisingmercaptan derivatives to convert the mercaptan derivatives to disulfidesand regenerated caustic.
 12. A process for refining fuel gas comprising:contacting a fuel gas with an amine compound to remove hydrogen sulfide(H₂S), carbon dioxide (CO₂), or both therefrom and produce an aminetreated fuel gas comprising an amine compound; contacting the aminetreated fuel gas with water to remove at least a portion of the aminecompound therefrom and produce a washed fuel gas; contacting the washedfuel gas with a either a caustic to remove acid gas or a blend of acaustic and an amine to remove both acid gas and carbonyl sulfide (COS)from the washed fuel gas and produce a caustic treated fuel gascomprising residual amine and residual caustic; contacting the caustictreated fuel gas with water to remove residual amines and residualcaustic therefrom and produce a rewashed fuel gas substantially free ofamine and caustic; and removing mercaptans from the rewashed fuel gas.13. The process of claim 12, wherein contacting the fuel gas with waterin a first water wash stage further comprises contacting the fuel gasand water with a coalescing material.
 14. The process of claim 12,wherein contacting the caustic treated fuel gas with water in a secondwater wash stage further comprises contacting the caustic treated fuelgas with a coalescing material, which may be the same or different fromthe coalescing material in the first water wash stage.
 15. The processof claim 12, wherein contacting a fuel gas with an amine compound toremove hydrogen sulfide (H₂S), carbon dioxide (CO₂), or both therefromcomprises selecting and using, as the amine, one or more compoundschosen from: monoethanolamine, diethanolamine, diglycolamine, methyldiethanolamine (MDEA), MDEA-based solvents, and diisopropylamine.
 16. Asystem for refining liquefied petroleum gas (LPG) comprising: a firstwater wash vessel; a caustic wash vessel in fluid communication with,and located downstream of, the first water wash vessel; and a secondwater wash vessel in fluid communication with, and located downstreamof, the caustic wash vessel.
 17. The system of claim 16, wherein thefirst water wash vessel comprises an interior and a coalescing materialpositioned within the interior.
 18. The system of claim 16, wherein thesecond water wash vessel comprises an interior and a coalescing materialpositioned within the interior, wherein the coalescing material may bethe same or different from the coalescing material of the first waterwash vessel.
 19. The system of claim 16, further comprising an absorberwherein the first water wash vessel is in fluid communication with, andlocated downstream of, the absorber.
 20. The system of claim 16, furthercomprising mercaptan removal apparatus.